Hyperprolactinemia is known to suppress gonadotropin secretion. While many studies have described the hypothalamic control of gonadotropin release during hyperprolactinemia, very little information exists concerning the effects of elevated prolactin on gonadotrope intracellular changes (dynamics). Only monitoring serum or pituitary concentrations of gonadotropins will not give a complete understanding of their synthesis and regulation within the gonadotropes. Therefore, in order to more accurately study the synthesis, release, and prolactin-induced suppression of LH and FSH, quantitative electron microscopy (morphometry) will be used and correlated with pituitary and serum levels of these hormones, as well as the hypothalamic concentration of LHRH, and serum 17-beta estradiol and progesterone. The project is designed to ascertain the effects of elevated prolactin on rat gonadotrope organelle dynamics during: a. the rat estrous cycle; b. ovariectomy (a time of stimulated gonadotrope synthesis); and c. a period of "recovery" from prolactin-induced gonadotropin suppression. Elevated prolactin levels will be induced by either: a. pituitary transplants beneath the kidney capsule; b. implantation of the MtTW15 prolactin-secreting tumor; c. administration of exogenous prolactin; or d. the use of a suckling rat model. These studies will provide new knowledge concerning the synthesis, secretion, and suppression of the gonadotropins during hyperprolactinemia, and could possibly reveal control points within the gonadotropes affected by elevated prolactin.